Steam is useful in a variety of industrial applications such as petroleum or chemical plants. Traditionally, stream is produced using a boiler, wherein a fuel is combusted to supply the heat needed to convert water to steam. Environmental regulations require reduced emissions of nitrogen oxides (NOx), such as nitric oxide (NO) and nitrogen dioxide (NO2), from combustion processes and equipment such as steam boilers. Thus, a need exists for improved combustion processes and equipment that reduces the amount of NOx emissions in the flue gas, especially to ultra-low levels below about 10 parts per million by volume (PPMv).